1. Field of the Invention
The present invention relates to a probability distribution constructing method and apparatus that constructs, based on plural images obtained by repeatedly photographing a field using a fixedly disposed camera, an appearance probability distribution of a size of a subject of a specific type that repeatedly appears having various sizes in the plural images, a storage medium of a probability distribution constructing program that allows a computer to operate as the probability distribution constructing apparatus, and also to a subject detecting method and apparatus that detects a subject using the appearance probability distribution, and a storage medium of a subject detecting program that allows the computer to operate as the subject detecting apparatus.
2. Description of the Related Art
In general, security cameras have been disposed in convenience stores or banks as one of security countermeasures. Moving picture images that are photographed by the security cameras have been displayed on a display screen of a monitoring room or the like and have been recorded. The moving images have been used to specify a criminal when a crime occurs.
In the past, the moving images that are photographed by the security cameras have been recorded as analog data. However, in recent years, the moving images have been recorded as digital data, for convenience of management. In addition, in the security cameras that have the above-described usage purpose, the moving images that are photographed over a long period of time need to be recorded, but there is a limitation in a recording capacity of a recording device that records the moving images. For this reason, when the moving images are recorded, a compressing process is applied to the moving images. Meanwhile, if the compressing process is applied to the moving images, the moving images may become unclear. If the moving images become unclear, it may be difficult to precisely grasp the situation of an event or specify a person from the moving images.
In recent years, in a field of an imaging apparatus such as digital cameras, with the development of a hardware technique of the imaging apparatus, a software technique of the imaging apparatus has been developed. One example of the software technique is a technique for detecting a face portion of a person in a photographing view angle, that is, a so-called face detecting technique. In the face detecting technique, generally, face parts, such as eyes, a nose, and a mouth, which form the face portion in the photographing view angle, are detected, and the face portion in the photographing view angle is detected on the basis of the detected face parts (for example, refer to Japanese Patent Application Publication No. 2007-188419).
If the face detecting technique is applied to the security camera, it is possible to detect a face portion of a person in a photographing view angle, when the moving images are taken. In addition, when the moving images are recorded, a high compressing process can be applied only to an area other than the detected face portion. In this way, it is conceivable to realize a security camera capable to obtaining a recorded moving image in which the face portion of a person in is clear, which makes it possible to readily specify a person who faced the security camera.
In this case, in order to effectively utilize moving images taken by the security cameras for the purpose of specifying the person, it is important to specify not only a person who is facing the security camera, but also a person whose back is directed to the security camera. This requires, besides the detection of the face portion of a person, that is, the front of the person, the detection of the head portion of the person including the front, flanks, and back of the person. If the head portion can be detected in moving images, it is possible to follow the detected head portion within a photographing view angle, which is largely effective when specifying a person.
In this case, when the face portion or the head portion of the person in the photographing view angle is detected, it is important to improve detection precision by suppressing the probability of erroneous detection. That is, it is necessary to improve the detection precision not only based on detection information of the face portion or the head portion but also on the basis of a variety of information about an environment around the face portion or the head portion.